Yet investors are hardly deterred. The restaurant-delivery startup just raised another $385 million from new and old backers to help make it more efficient than ever.

“This investment will take us to the next level,” says founder and former investment banker William Shu. To date he’s raised $860 million for the company.

After just four years in business, Deliveroo is now worth $2 billion.

What do investors see in the startup? Two things, according to Martin Mignot, who just led Index Ventures' fifth round of investment in the company:

First, Deliveroo’s customers are repeatedly using the service, and some are starting to see it as an alternative to buying groceries and making dinner.

“The takeaway market is X billion, but the grocery market is 100 times that,” Mignot says. Down the line he thinks Deliveroo’s customers will be using it multiple times a week -- maybe even multiple times a day -- to eat meals.

Secondly, the startup’s thousands of riders, mostly on bikes, are squeezing in more deliveries per hour. Deliveroo is obsessed with efficiency, says Mignot. “It’s how you increase the income of your riders, and how you improve your margins,” he says.

Deliveroo’s riders can choose to be paid by the hour or per delivery; in the latter case, they get £3.75 per drop-off. On average, they're making about three deliveries an hour, according to a spokesman.

More drop-offs means more money, which should make Deliveroo more attractive to riders than Amazon Restaurants or Uber Eats. And riders like the flexibility, Mignot says. Just last night he ordered sushi from a local restaurant and noticed his Deliveroo rider had parked up in a rental bike.

Slowly but surely, Deliveroo is getting those order times down. In January, the startup said it was cutting customer wait times by 20% to an average 29 minutes, by using predictive software.

Its new algorithm, called Frank, is a little like Uber’s complex logistical software that matches riders with food orders. It uses "machine-learning predictive models" of when food will be ready and which rider has the best vehicle and location to deliver it. Nowadays, riders spend an average six minutes traveling with food, the company says.

Along with beefing up its software, Deliveroo is spending the new $385 million on its bricks-and-mortar strategy: expanding a network of standalone kitchens that restaurants can use as delivery hubs.

“We're live in 21 kitchens, with a further 49 set to launch in the coming weeks across our new London locations,” a spokesman said of the service called Editions.

These new kitchens dotted across London, don't just extend a restaurant's reach to delivering to new customers - they also deliver 24% more quickly than the original restaurants do, the spokesman said. The kitchens, which Deliveroo kits out itself, have "increased sales in restaurants by up to 400%" he added.

Over time, these efficiencies should improve Deliveroo’s gross margins, which stood at a paltry 0.7% in 2016.

Mignot of Index says Deliveroo’s observers and critics are too “obsessed” with margins, and the company's efficiency metrics are more important.

At least one potential investor disagrees.

Mark Tluszcz of Mangrove Capital Partners, an early backer of Skype, warns that Deliveroo’s margins are much too thin to sustain a business.

The looming problem is that Deliveroo operates in a region where regulators are pushing for it to pay riders more benefits like sick pay. The company is fielding several lawsuits over employment rights, and changes in the law could cost the company much more.

The big question is whether Deliveroo’s efficiency hacks -- the clever new algorithms, and the new kitchens -- will be enough to offset any extra employment costs that lie ahead.